Small format interchangeable core (SFIC) locks are widely known in the industry. The concept allows mechanical cylinders to be removed from lock housings by the use of a specially bitted mechanical control key and re-installed into different housings. This can be done quickly and eliminates the need to have the mechanical cylinders rekeyed or re-pinned.
A feature of the mechanical SFIC lock is a control element, such as a control sleeve, that includes features that selectively lock the lock within a housing, such as a radial projection, or lug, that extends into a groove formed on the interior of the locking housing to engage the interchangeable cylinder core into the locking housing and lock the cylinder in place. When a properly bitted control key is inserted into the keyway of the interchangeable core and rotated, the control sleeve is rotated with the plug of the cylinder core into a retracted position to withdraw the projection from the groove and release the interchangeable core from the lock housing, thereby allowing the core to be removed from the lock housing. Keys bitted for normal access at the SFIC lock are able to rotate the cylinder plug and open the lock but are not able to rotate the control sleeve with the plug.
When developing an electronic SFIC lock retrofit for existing SFIC housings, a feature must be provided to allow the same function of inserting and removing SFIC cores. That is, a control element and means for actuating the control element must be provided so that the SFIC lock can be locked within and removed from the lock housing.
One SFIC electronic cylinder is described in U.S. Pat. No. 6,604,394. The core described in the '394 patent includes a control sleeve that is blocked from retracting by a spring biased blocking pin. Removal of the core requires a specially-shaped control key that has an extension on the key tip that, when the key is inserted into the cylinder, extends into the cylinder and raises the blocking pin out of the path of the control sleeve and allows the control sleeve to rotate in conjunction with the plug of the lock core to a retracted position. Normal access keys lack the extension on the key tip, and thus do not engage the control sleeve blocking pin when used to open the SFIC electronic cylinder. Like the normal access keys, the special control key must be programmed for access to the SFIC electronic cylinder in order to rotate the plug, but the engagement with the control sleeve is entirely a function of the mechanical portion of the key tip. No key programming is provided to differentiate the control key from the normal access key.
This mechanical approach to controlling rotation of the control sleeve represents a critical security flaw. Any normal access key programmed to operate the SFIC electronic cylinder could be used, in conjunction with picking tools able to raise the control sleeve blocking pin, to remove the core and leave the door unsecured. While the key and lock audit would capture the opening of the cylinder, there would be no subsequent audit of entries while the cylinder was removed from the door.